U.S. patent application number 11/035074 was filed with the patent office on 2005-09-08 for heat shrinkable polyester film.
Invention is credited to Hashimoto, Masatosi, Ito, Hideki, Mukouyama, Yukinobu, Oko, Tsutomu, Tabota, Norimi.
Application Number | 20050196563 11/035074 |
Document ID | / |
Family ID | 27520261 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050196563 |
Kind Code |
A1 |
Ito, Hideki ; et
al. |
September 8, 2005 |
Heat shrinkable polyester film
Abstract
A heat shrinkable polyester film of the present invention has a
transverse tear defect percentage of about 20% or less as
determined in the following vibration test: the film is rolled into
a tubular shape, two of its opposite edges bonded together, and
then the tubular film is placed around a vertical stack (total
weight: 660 g) of three food container cans each having a diameter
of 72 mm and a height of 55 mm; the can stack with the tubular film
placed therearound is passed through a shrink tunnel to shrink the
tubular film onto the can stack; a total of 18 packs of such can
stacks are placed into a cardboard box having a length of 455 mm, a
width of 230 mm and a height of 165 mm (6 packs in the length
direction by 3 packs in the width direction), and the cardboard box
is sealed; the cardboard box is vibrated along the width direction
for 30 min by a stroke of 50 mm and at a vibration rate of 180
reciprocations/min, after which the transverse tearage of the
tubular film is visually observed; and the transverse tear defect
percentage (%) is determined based on the number of defective packs
per 18 packs, wherein the defective pack is any pack having a tear
flaw of 30 mm or longer along a can periphery. The heat shrinkable
polyester film of the present invention has a good shock resistance
during shipping especially under low temperatures, with a good
finish after shrinkage and a sufficient solvent adhesiveness. Thus,
the heat shrinkable polyester film of the present invention is
suitable for use in a multi-packaging label for packaging, inter
alia, a stack of cans.
Inventors: |
Ito, Hideki; (Inuyama-shi,
JP) ; Hashimoto, Masatosi; (Inuyama-shi, JP) ;
Mukouyama, Yukinobu; (Inuyama-shi, JP) ; Tabota,
Norimi; (Inuyama-shi, JP) ; Oko, Tsutomu;
(Inuyama-shi, JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET NW
SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
27520261 |
Appl. No.: |
11/035074 |
Filed: |
January 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11035074 |
Jan 14, 2005 |
|
|
|
09492173 |
Jan 27, 2000 |
|
|
|
Current U.S.
Class: |
428/34.1 |
Current CPC
Class: |
Y10T 428/13 20150115;
C08J 5/18 20130101; C08J 2367/02 20130101 |
Class at
Publication: |
428/034.1 |
International
Class: |
B32B 001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 1999 |
JP |
11-020836 |
Mar 8, 1999 |
JP |
11-060898 |
Apr 23, 1999 |
JP |
11-117338 |
Apr 23, 1999 |
JP |
11-117339 |
Apr 23, 1999 |
JP |
11-117340 |
Claims
What is claimed is:
1. A heat shrinkable polyester film having a transverse tear defect
percentage of about 20% or less as determined in the following
vibration test: the film is rolled into a tubular shape, two of its
opposite edges bonded together, and then the tubular film is placed
around a vertical stack (total weight: 660 g) of three food
container cans each having a diameter of 72 mm and a height of 55
mm; the can stack with the tubular film placed therearound is
passed through a shrink tunnel to shrink the tubular film onto the
can stack; a total of 18 packs of such can stacks are placed into a
cardboard box having a length of 455 mm, a width of 230 mm and a
height of 165 mm (6 packs in the length direction by 3 packs in the
width direction), and the cardboard box is sealed; the cardboard
box is vibrated along the width direction for 30 min by a stroke of
50 mm and at a vibration rate of 180 reciprocations/min, after
which the transverse tearage of the tubular film is visually
observed; and the transverse tear defect percentage (%) is
determined based on the number of defective packs per 18 packs,
wherein the defective pack is any pack having a tear flaw of 30 mm
or longer along a can periphery.
2. A heat shrinkable polyester film according to claim 1, wherein
the film has a longitudinal refractive index Nx and a transverse
refractive index Ny which satisfy the following expressions (1) and
(2): 1.561<Nx<1.566 (1); and 0.040<Ny-Nx<0.070 (2).
3. A heat shrinkable polyester film according to claim 1, wherein
the film has a shrinkage of about 50% or more along its main
shrinkage direction when the film is put in hot water of 95.degree.
C. for 10 sec.
4. A heat shrinkable polyester film according to claim 1, wherein
the film has a shrinkage of about 10% to about 25% along a
direction perpendicular to its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 10 sec.
5. A heat shrinkable polyester film according to claim 1, wherein
the film has a solvent adhesiveness with 1,3-dioxolane.
6. A heat shrinkable polyester film according to claim 1, wherein
the film can be used as a multi-packaging film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a heat shrinkable polyester
film, and particularly to a heat shrinkable polyester film suitable
for use in a label. More particularly, the present invention
relates to a heat shrinkable polyester film for use in a
multi-packaging label for packaging, inter alia, a stack of cans,
which has a good shock resistance during shipping, especially under
low temperatures, with a good finish after shrinkage and a
sufficient solvent adhesiveness (i.e., an adhesive property of the
film provided by application of a solvent thereon). The present
invention further relates to a heat shrinkable polyester film for
use in a cap sealing label for a bottle container (e.g., a milk
bottle), in which a bonded portion (backlining portion) of the
label (i.e. a portion of a tubular label where two opposite edges
of the material film sheet are bonded together) has a high adhesive
retention after shrinkage and which has very little creasage,
shrinkage non-uniformity, distortion, or jumping occurring from a
shrinkage process.
[0003] 2. Description of the Related Art
[0004] Heat shrinkable films made of polyvinyl chloride,
polystyrene, or the like, have been widely used in the field of
multi-packaging films for use in packaging a stack of cans. In
recent years, heat shrinkable polyester films have been attracting
public attention as more problems have been found to exist with the
former materials. That is, polyvinyl chloride products generate a
chlorine gas when incinerated, and it is difficult to print on
polystyrene products.
[0005] However, when a stack of articles is shrink-packaged with a
label of a conventional heat shrinkable polyester film, a flaw is
likely to occur due to, for example, a shock applied when the
article stack hits another article stack during shipping or a
friction between the article stack and the outer packaging box
therearound. Moreover, because such a conventional film is drawn in
one direction in the production process, the film is likely to be
torn for a substantial length along its main shrinkage direction,
in which case the film can no longer hold articles therein, thereby
detracting from the commercial value of the articles. Even a
state-of-the-art multi-packaging polyvinyl chloride film, which is
supposed to be flexible and tear-resistant, may be torn especially
under low temperatures.
[0006] One possible way to prevent such tearing along a particular
direction is to orient a film along a direction perpendicular to
its main shrinkage direction as well as the main shrinkage
direction. However, when the film is oriented along these two
directions with a poor balance between the directions, the film may
be shrunk with a poor balance between the directions, thereby
resulting in a poor finish after shrinkage. Moreover, when a tube
is produced from the film by using an environmentally preferred
chlorine-free solvent, a sufficient solvent adhesiveness cannot be
obtained.
[0007] In recent years, a container (e.g., a bottle) for beverage,
food, etc., is provided with a so-called "cap seal" wrapped around
the cap or lid of the container. The cap seal is provided not only
for decorative purposes but also for purposes of preventing someone
from mixing poison into the contained product. A heat shrinkable
film of polyvinyl chloride, polystyrene, or the like, has been
widely used in a cap sealing label, as in a general purpose label.
However, as already noted above, more problems have been found to
exist with these materials (polyvinyl chloride products generate a
chlorine gas when incinerated, and it is difficult to print on
polystyrene products). Moreover, in order to effectively recycle
PET bottles, it is necessary to collect non-PET labels made of
polyvinyl chloride, polystyrene, etc., separately from PET labels.
Thus, there is a need for cap sealing labels made of these
environmentally preferred polyester heat shrinkable films.
[0008] A cap seal may be produced as follows. First, a sheet of
heat shrinkable film having a predetermined size is rolled into a
tubular shape with two of its opposite edges bonded together. Then,
the tubular film is cut into smaller tubular label pieces.
[0009] There are two ways as follows that are typically employed in
cap sealing processes. One way is to directly place a label
produced as described above around the container and shrink the
label onto the container. The other way is to first shrink the
label onto a metal mold to provide a "preform" product, and then
further shrink the label onto the container. In either case, when
the label is heat-shrunk, the bonded portion (backlining portion)
of the label desirably stays bonded together. If the bonded portion
falls apart, the productivity decreases substantially.
[0010] Moreover, the shape characteristics of the label after it is
heat-shrunk are also important. It is undesirable that the label
does not shrink enough, or the shrunk label has creasage,
shrinkage. non-uniformity, distortion, or jumping. Particularly
when the label is used for a food container, it is in many cases
undesirable for the label to get moist. Therefore, in such a case,
the heat shrinkage process is typically done using hot air instead
of steam. When using hot air, however, the heat efficiency is lower
than that when using steam, whereby it is likely that the film does
not shrink enough, or the shrunk label has creasage, shrinkage
non-uniformity, distortion.
[0011] When the heat shrinkable film is used as a cap'sealing label
with nothing printed thereon, in many cases, the film is also
required to have transparency.
SUMMARY OF THE INVENTION
[0012] According to one aspect of this invention, a heat shrinkable
polyester film has a transverse tear defect percentage of about 20%
or less as determined in the following vibration test: the film is
rolled into a tubular shape, two of its opposite edges bonded
together, and then the tubular film is placed around a vertical
stack (total weight: 660 g) of three food container cans each
having a diameter of 72 mm and a height of 55 mm; the can stack
with the tubular film placed therearound is passed through a shrink
tunnel to shrink the tubular film onto the can stack; a total of 18
packs of such can stacks are placed into a cardboard box having a
length of 455 mm, a width of 230 mm and a height of 165 mm (6 packs
in the length direction by 3 packs in the width direction), and the
cardboard box is sealed; the cardboard box is vibrated along the
width direction for 30 min by a stroke of 50 mm and at a vibration
rate of 180 reciprocations/min, after which the transverse tearage
of the tubular film is visually observed; and the transverse tear
defect percentage (%) is determined based on the number of
defective packs per 18 packs, wherein the defective pack is any
pack having a tear flaw of 30 mm or longer along a can
periphery.
[0013] In one embodiment of the invention, the film has a
longitudinal refractive index Nx and a transverse refractive index
Ny which satisfy the following expressions (1) and (2):
1.561<Nx<1.566 (1); and
0.040<Ny-Nx<0.070 (2)
[0014] In one embodiment of the invention, the film has a shrinkage
of about 50% or more along its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 10 sec.
[0015] In one embodiment of the invention, the film has a shrinkage
of about 10% to about 25% along a direction perpendicular to its
main shrinkage direction when the film is put in hot water of
95.degree. C. for 10 sec.
[0016] In one embodiment of the invention, the film has a solvent
adhesiveness with 1,3-dioxolane.
[0017] In one embodiment of the invention, the film can be used as
a multi-packaging film.
[0018] According to another aspect of this invention, a heat
shrinkable polyester film is provided, wherein: the film has a
shrinkage of about 10% to about 40% along its main shrinkage
direction when the film is put in hot water of 70.degree. C. for 5
sec; the film has a shrinkage of about 50% or more along its main
shrinkage direction when the film is put in hot water of 95.degree.
C. for 5 sec; the film has a shrinkage of about 10% or less along a
direction perpendicular to its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 5 sec; and when the
film is formed into a label having a bonded portion, the bonded
portion of the label has an adhesive retention of about 95% or more
after shrinkage.
[0019] In one embodiment of the invention, the bonded portion of
the label has an adhesive retention of about 97% or more after
shrinkage.
[0020] In one embodiment of the invention, the bonded portion of
the label has an adhesive retention of about 99% or more after
shrinkage.
[0021] In one embodiment of the invention, the bonded portion of
the label has an adhesive retention of about 99.5% or more after
shrinkage.
[0022] In one embodiment of the invention, the label is a tubular
label formed by bonding together two of opposite edges of a
rectangular sheet of the film.
[0023] In one embodiment of the invention, the bonded portion is a
portion of a tubular label made of a rectangular sheet of the film
where two of its opposite edges are bonded together.
[0024] In one embodiment of the invention, the film is a cap
sealing heat shrinkable polyester film.
[0025] According to still another aspect of this invention, there
is provided a cap sealing label made of a heat shrinkable polyester
film as defined above.
[0026] According to still another aspect of this invention, a heat
shrinkable polyester film is provided, wherein: the film has a
shrinkage of about 10% to about 40% along its main shrinkage
direction when the film is put in hot water of 70.degree. C. for 5
sec; the film has a shrinkage of about 50% or more along its main
shrinkage direction when the film is put in hot water of 95.degree.
C. for 5 sec; the film has a shrinkage of about 10% or less along a
direction perpendicular to its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 5 sec; the film has a
film haze of about 3% to 15 about 10% for a film thickness of 50
.mu.m: and when the film is formed into a label having a bonded
portion, the bonded portion of the label has an adhesive retention
of about 95% or more after shrinkage.
[0027] In one embodiment of the invention, the label is a tubular
label formed by bonding together two of opposite edges of a
rectangular sheet of the film.
[0028] In one embodiment of the invention, the bonded portion is a
portion of a tubular label made of a rectangular sheet of the film
where two of its opposite edges are bonded together.
[0029] In one embodiment of the invention, the film is a cap
sealing heat shrinkable polyester film.
[0030] According to still another aspect of this invention, there
is provided a cap sealing label made of a heat shrinkable polyester
film as defined above.
[0031] According to still another aspect of this invention, there
is provided a heat shrinkable polyester film, wherein: the film has
a shrinkage of about 10% to about 40% along its main shrinkage
direction when the film is put in hot water of 70.degree. C. for 5
sec; the film has a shrinkage of about 50% or more along its main
shrinkage direction when the film is put in hot water of 95.degree.
C. for 5 sec; the film has a shrinkage of about 10% or less along a
direction perpendicular to its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 5 sec; the film has a
shrinkage of about 15% to about 30% along its main shrinkage
direction when the film is put in hot water of 80.degree. C. for 5
sec after a preform process; and when the film is formed into a
label having a bonded portion, the bonded portion of the label has
an adhesive retention of about 95% or more after shrinkage.
[0032] In one embodiment of the invention, the label is a tubular
label formed by bonding together two of opposite edges of a
rectangular sheet of the film.
[0033] In one embodiment of the invention, the bonded portion is a
portion of a tubular label made of a rectangular sheet of the film
where two of its opposite edges are bonded together.
[0034] In one embodiment of the invention, the film is a cap
sealing heat shrinkable polyester film.
[0035] According to still another aspect of this invention, there
is provided a cap sealing label made of a heat shrinkable polyester
film as defined above.
[0036] According to still another aspect of this invention, there a
heat shrinkable polyester film is provided, wherein: the film has a
shrinkage of about 10% to about 40% along its main shrinkage
direction when the film is put in hot water of 70.degree. C. for 5
sec; the film has a shrinkage of about 50% or more along its main
shrinkage direction when the film is put in hot water of 95.degree.
C. for 5 sec; the film has a shrinkage of about 10% or less along a
direction perpendicular to its main shrinkage direction when the
film is put in hot water of 95.degree. C. for 5 sec; the film has a
preform finish defective percentage of about 1% or less; and when
the film is formed into a label having a bonded portion, the bonded
portion of the label has an adhesive retention of about 95% or more
after shrinkage.
[0037] In one embodiment of the invention, the label is a tubular
label formed by bonding together two of opposite edges of a
rectangular sheet of the film.
[0038] In one embodiment of the invention, the bonded portion is a
portion of a tubular label made of a rectangular sheet of the film
where two of its opposite edges are bonded together.
[0039] In one embodiment of the invention, the film is a cap
sealing heat shrinkable polyester film.
[0040] According to still another aspect of this invention, there
is provided a cap sealing label made of a heat shrinkable polyester
film as defined above.
[0041] Thus, the invention described herein makes possible the
advantages of: (1) providing a heat shrinkable polyester film which
has a good shock resistance during shipping especially under low
temperatures, with a good finish after shrinkage and a sufficient
solvent adhesiveness; (2) providing a heat shrinkable polyester
film having such properties for use in a multi-packaging label for
packaging, inter alia, a stack of cans; and (3) providing a heat
shrinkable polyester film for use in a cap sealing label for a
bottle container, in which a bonded portion (backlining portion) of
the label has a high adhesive retention after shrinkage and which
has very little creasage, shrinkage non-uniformity, distortion, or
jumping occurring from a shrinkage process.
[0042] These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and
understanding the following detailed description with reference to
the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a schematic diagram illustrating a vibration test
for a heat shrinkable polyester film;
[0044] FIG. 2 is a diagram illustrating a vibration test for a heat
shrinkable polyester film;
[0045] FIG. 3 is a diagram illustrating a case where a tear flaw
has occurred in a film along a can periphery;
[0046] FIG. 4A is a perspective view illustrating a label produced
by rolling a sheet of heat shrinkable film into a tubular shape
with two of its opposite edges bonded together, and then cutting
the tubular film into smaller pieces;
[0047] FIG. 4B is a perspective view illustrating the label being
placed around a metal cylinder; and
[0048] Each of FIGS. 5A to 5E is a perspective view illustrating
the appearance of the label after shrinking (i.e., the preform
finish property).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] A heat shrinkable polyester film according to an embodiment
of the present invention will now be described.
[0050] (Heat Shrinkable Polyester Film Suitable for use as
Multi-Packaging Film)
[0051] Preferred polyesters for use in a heat shrinkable polyester
film of the present invention suitable for use as a multi-packaging
film typically include polyethylene terephthalate, polyethylene
naphthalate, and other polyesters obtained by copolymerizing such
polyesters with an acid component or a long-chain glycol component
of an aliphatic compound.
[0052] According to the present invention, in addition to the acid
components of the polyester comprising terephthalic acid or
naphthalenedicarboxylic acid, it is possible to use one or more
known dicarboxylic acids such as oxalic acid, malonic acid,
succinic acid, adipic acid, azelaic acid, isophthalic acid,
decanedicarboxylic acids, and dimeracid. Moreover, in addition to
the diol component comprising butanediol, it is possible to use one
or more known diols such as ethylene glycol, neopentyl glycol,
hexamethylene glycol, 1,4-cyclohexane dimethanol, dimer acid diol,
and ethylene-oxide-added tetramethylene glycol.
[0053] In order to obtain a heat shrinkable polyester film which is
determined to be desirable in a vibration test, it is preferred to
use neopentyl glycol as one of the diol components.
[0054] Moreover, in order to improve the smoothness of the heat
shrinkable polyester film, the film preferably contain an inorganic
lubricant and/or an organic lubricant. Optionally, the film may
contain further additives such as a stabilizer, a coloring agent,
an antioxidant, a defoamer, and an antistatic agent.
[0055] The heat shrinkable polyester film of the present invention
is required to have a transverse tear defect percentage of about
20% or less, and preferably about 10% or less, as determined in a
vibration test. When the transverse tear defect percentage exceeds
20%, the film is likely to have many tears during actual
shipping.
[0056] In the present invention, it is further preferred that the
refractive indices Nx, Ny of the film satisfy the following
expressions (1) and (2):
1.561<Nx<1.566 (1); and
0.040<Ny-Nx<0.070 (2).
[0057] The more preferred range of the refractive index Nx is 1.562
to 1.565. The more preferred range of the value (Ny-Nx) is 0.050 to
0.060. When the refractive index Nx is less than 1.561, the
strength of the film against transverse tears may be insufficient.
When the refractive index Nx exceeds 1.566, the shrinkage of the
film along a direction perpendicular to the main shrinkage
direction increases, thereby decreasing the shrunk finish
property.
[0058] When the value (Ny-Nx) is less than 0.040, the shrinkage
balance between the longitudinal direction and the transverse
direction of the film may be poor, resulting in shrinkage
non-uniformity. When the value (Ny-Nx) exceeds 0.070, the
transverse tear defect percentage increases.
[0059] Preferably, the film of the present invention has a
shrinkage of about 50% or more, and more preferably about 55% or
more, along its main shrinkage direction when the film is put in
hot water of 95.degree. C. for 10 sec. When the hot water shrinkage
along the main shrinkage direction is less than 50%, it is likely
that the film does not shrink enough, or the shrunk label has
shrinkage non-uniformity, thereby resulting in a poor finish.
[0060] Preferably, the film of the present invention has a
shrinkage of about 10% to about 25%, and more preferably about 10%
to about 20%, along a direction perpendicular to its main shrinkage
direction when the film is put in hot water of 95.degree. C. for 10
sec. When the hot water shrinkage along this direction is less than
10%, the strength of the film against transverse tears may be
insufficient. When hot water shrinkage along this direction exceeds
25%, the shrunk film may have shrinkage non-uniformity or jumping,
thereby resulting in a poor finish.
[0061] Preferably, the film of the present invention has a solvent
adhesiveness with 1,3-dioxolane.
[0062] In order to achieve the objects of the present invention, a
polyester film having its main shrinkage direction along the
transverse (or width) direction is more practical. Therefore, an
exemplary film production method where the film has its main
shrinkage direction along the transverse direction will be
described below. However, it is understood that the present
invention is also applicable to a case where the film has its main
shrinkage direction along the longitudinal direction.
[0063] According to the present invention, a polyester material is
first dried by using a dryer or vacuum dryer such as a hopper dryer
or a paddle dryer. Then, the polyester. material is extruded at a
temperature of 200.degree. C. to 300.degree. C., and rapidly cooled
to obtain an undrawn film. In order to produce a heat shrinkable
polyester film having its main shrinkage direction along the
transverse direction, the obtained undrawn film is typically drawn
longitudinally by a drawing factor of 1.1 to 1.3 at 80.degree. C.
to 95.degree. C., and then drawn laterally by a drawing factor of 3
to 5 at 70.degree. C. to 85.degree. C. It is understood that any
other drawing condition may alternatively be set for this
process.
[0064] (Heat Shrinkable Polyester Film Suitable for use in Cap
Sealing Label)
[0065] A heat shrinkable polyester film of the present invention
suitable for use in a cap sealing label is preferably produced from
a polyester composition containing a polyester comprising a
dicarboxylic acid component and a diol component, and a polyester
elastomer. The polyester composition may contain 50 wt % to 99.9 wt
% of a polyester, and may contain 0.1 wt % to 50 wt % of a
polyester elastomer.
[0066] The heat shrinkable polyester film of the present invention
can be produced by drawing the undrawn film obtained from the
above-described polyester composition at a temperature equal to or
greater than Tg-5.degree. C. and less than Tg+15.degree. C. (where
Tg is the glass-transition temperature of the polyester) along the
transverse direction (direction perpendicular to the extrusion
direction) by a drawing factor of 3.0 or more, and preferably 3.5
or more.
[0067] (Polyester)
[0068] The dicarboxylic acid component of the polyester may include
aromatic dicarboxylic acids (e.g., terephthalic acid, isophthalic
acid, naphthalenedicarboxylic acid, and orthphthalic acid),
aliphatic dicarboxylic acids (e.g., adipic acid, azelaic acid,
sebacic acid, and decanedicarboxylic acids), alicyclic dicarboxylic
acids, or the like.
[0069] Where the polyester contains an aliphatic dicarboxylic
acid(s) (e.g., adipic acid, sebacic acid, decanedicarboxylic acid,
or the like), the content of the aliphatic dicarboxylic acid is
preferably less than 3 mol % (this applies to all the dicarboxylic
acid components used). A heat shrinkable polyester film obtained by
using a polyester which contains 3 mol % or more of such an
aliphatic dicarboxylic acid(s) may not have a sufficient rigidity
in high-speed processes.
[0070] The polyester preferably does not contain a polyvalent
carboxylic acid whose valence is 3 or more (e.g., a trimellitic
acid, a pyromellitic acid, or anhydride thereof). If the polyester
contains such a polyvalent carboxylic acid, the content thereof is
preferably 3 mol % or less. With a heat shrinkable polyester film
obtained by using a polyester containing such a polyvalent
carboxylic acid, a sufficient shrinkage may not be achieved.
[0071] A diol component of the polyester to be used in the present
invention may include aliphatic diols (e.g., ethylene glycol,
propane diol, butane diol, neopentyl glycol, hexane diol, or the
like), alicyclic diols (e.g., 1,4-cyclohexane dimethanol), aromatic
diols, or the like.
[0072] A polyester used in the heat shrinkable polyester film of
the present invention is preferably a polyester whose
glass-transition temperature (Tg) is adjusted to 60.degree. C. to
75.degree. C. by mixing therein one or more diols whose carbon
number is 3 to 6 (e.g., propane diol, butane diol, neopentyl
glycol, and hexane diol).
[0073] In order to obtain a heat shrinkable polyester film having a
particularly desirable shrunk finish property, it is preferred to
use neopentyl glycol as one of the diol components, preferably in
an amount of 15 mol % to 25 mol % (this applies to all the diol
components used).
[0074] It is preferable not to include a diol whose carbon number
is 8 or more (e.g., octanediol) or a polyalcohol whose valence is 3
or more (e.g., trimethylolpropane, trimethylolethane, glycerin, and
diglycerin). If such a diol or such a polyalcohol is included, the
content thereof is preferably 3 mol % or less. With a heat
shrinkable polyester film obtained by using a polyester containing
such a diol or such a polyalcohol, a sufficient shrinkage may not
be achieved.
[0075] The polyester preferably contains the least amount possible
of diethylene glycol, triethylene glycol, and polyethylene glycol.
Particularly, diethylene glycol is likely to be present because it
is a byproduct from a polyester polymerization process.
Nevertheless, in the polyester used in the present invention, the
content of diethylene glycol is preferably less than 4 mol %.
[0076] When two or more polyesters are mixed together, the acid
component content or the diol component content is the content with
respect to the acid component or the diol component, respectively,
of all the polyesters. These contents are irrespective of whether
ester interchange occurs after mixing.
[0077] The above-described polyesters can be produced by any
conventional method. For example, the polyester can be obtained by
using, for example, a direct esterification method, where a
dicarboxylic acid and a diol are directly reacted with each other,
or a transesterification method, where a dimethyl dicarboxylate and
a diol are reacted with each other. The polymerization may be
performed either in a batch process or a continuous process.
[0078] (Polyester Elastomer)
[0079] The polyester elastomer (polyester block copolymer) used in
the present invention is a polyester block copolymer comprising a
high melting point crystalline polyester segment (hard segment) and
a low melting point soft polymer segment having a molecular weight
of 400 or more (soft segment). When a high polymer is made solely
of the high melting point crystalline polyester segment, the
melting point is 200.degree. C. or more. The low melting point soft
polymer segment itself has a melting point or a softening point of
80.degree. C. or less.
[0080] When a fiber-forming high polymer is made solely of the high
melting point crystalline polyester segment (hard segment), the
melting point is 200.degree. C. or more.
[0081] For example, the high melting point crystalline polyester
segment may be: a polyester comprising a residue of an aromatic
dicarboxylic acid (e.g. , terephthalic acid, isophthalic acid,
1,5-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic
acid) and a residue of an aliphatic, aromatic or alicyclic diol
(e.g., ethylene glycol, propylene glycol, tetramethylene glycol,
pentamethylene glycol, 2,2-dimethyltrimethylene glycol,
hexamethylene glycol, decamethylene glycol, p-xylene glycol, and
cyclohexane dimethanol); a polyester comprising a residue of an oxy
acid (e.g., p-(.beta.-hydroxyethoxy)benzoa- te, and
p-oxybenzoatepibarolactone); a polyether ester comprising a residue
of an aromatic ether dicarboxylic acid (e.g.,
1,2-bis(4,4'-dicarboxymethylphenoxy)ethane,
di(4-carboxyphenoxy)ethane) and a residue of the above-described
aliphatic, aromatic or alicyclic diol; or a polyamide ester
comprising a residue of an aromatic amide dicarboxylic acid (e.g.,
bis (N-paracarboethoxyphenyl)terephthalimide) and a residue of the
above-described aliphatic, aromatic or alicyclic diol.
[0082] It is also possible to use a copolymer polyester containing
two or more of such dicarboxylic acid residues and/or diol
residues.
[0083] The low melting point soft polymer segment having a
molecular weight of 400 or more (soft segment) is a segment in a
polyester block copolymer which is substantially amorphous. The
segment itself has a melting point or a softening point of
80.degree. C. or less.
[0084] The molecular weight of the low melting point soft polymer
segment is 400 to 8000, and preferably 700 to 5000.
[0085] The ratio of the low melting point soft polymer segment in
the polyester elastomer is preferably 1 wt % to 90 wt %, and more
preferably 5 wt % to 80 wt %.
[0086] Typical low melting point soft polymer segments include a
polyether (e.g., polyethylene oxide glycol, polypropylene oxide
glycol, polytetramethylene oxide glycol, a glycol of a copolymer of
ethylene oxide and propylene oxide, and a glycol of a copolymer of
ethylene oxide and tetrahydrofuran), an aliphatic polyester (e.g.,
polyneopentyl azelate, polyneopentyl adipate, and poly-neopentyl
sebacate), polylactone (e.g., poly-.epsilon.-caprolactone), and the
like.
[0087] In view of the compatibility with the polyester included in
the polyester film, it is particularly preferred that the polyester
elastomer includes polylactone (e.g., poly-.epsilon.-caprolactone)
as the soft segment. With a better compatibility between the
polyester elastomer and the polyester, the film will have a better
transparency and the bonded portion (backlining portion) of the
label will have a better adhesion.
[0088] The polyester elastomer is contained in the polyester
composition of the polyester film in an amount of 0.1 wt % to 50 wt
%, preferably 0.1 wt % to 30 wt %, and more preferably 5 wt % to 30
wt %.
[0089] When the content of the polyester elastomer is less than 0.1
wt % or greater than 50 wt %, the bonded portion (backlining
portion) of the label produced from the polyester film of the
present invention will have a poor adhesion.
[0090] The same additives as those described above may be included
to improve the smoothness of the heat shrinkable film. The
inorganic lubricant may be, for example, titanium dioxide, fine
particle silica, kaoline, or calcium carbonate. The organic
lubricant may be, for example, long-chain fatty acid ester.
[0091] The hot water shrinkage of a heat shrinkable polyester film
can be determined as follows. The film is subjected to a no-load
treatment in hot water. Based on the length of the film before
shrinkage and that after shrinkage, the hot water shrinkage of the
film can be calculated by the expression:
Heat shrinkage=((length before shrinkage-length after
shrinkage)/length before shrinkage).times.100(%)
[0092] The heat shrinkable polyester film of the present invention
has a shrinkage of about 10% to about 40%, and preferably about 20%
to about 40%, along its main shrinkage direction when the film is
put in hot water of 70.degree. C. for 5 sec. The film has a
shrinkage of about 50% or more, and preferably about 50% to about
70%, along its main shrinkage direction when the film is put in hot
water of 95.degree. C. for 5 sec. The film has a shrinkage of about
10% or less, preferably about 8% or less, and more preferably about
6% or less, along a direction perpendicular to its main shrinkage
direction when the film is put in hot water of 95.degree. C. for 5
sec.
[0093] For a hot water shrinkage process at 70.degree. C. for 5
sec, when the shrinkage along the main shrinkage direction is less
than 10%, the low temperature shrinkage of the film may be
insufficient, whereby it may be necessary to increase the shrinkage
temperature, which is undesirable. When the shrinkage exceeds 40%,
jumping of the label may occur from the heat shrinkage process.
[0094] The shrinkage for a hot water shrinkage process at
95.degree. C. for 5 sec is preferably about 50% to about 70%. When
the shrinkage is less than 50%, it may be necessary to increase the
shrinkage temperature, which is undesirable. When the shrinkage
exceeds 70%, the label may still have a shrinking force even after
the heat shrinkage process, whereby the label is likely to
jump.
[0095] The heat shrinkable polyester film of the present invention
has a film haze of about 3% to about 10% for a film thickness of 50
.mu.m. When the haze exceeds 10%, there is a practical problem in
that the printed label may have a poor color. When the haze is less
than 3%, the film thickness distribution may deteriorate.
[0096] A label made of the heat shrinkable polyester film of the
present invention after a preform process has a hot water shrinkage
along the main shrinkage direction of about 15% to about 30%, and
more preferably about 17% to about 25% for a hot water shrinkage
process at 80.degree. C. for 5sec. When the hot water shrinkage
along the main shrinkage direction after the preform process is
less than 15%, insufficient shrinkage may occur. When the hot water
shrinkage is 30% or more, jumping of the label may occur from the
heat shrinkage process.
[0097] When the label made of the heat shrinkable polyester film of
the present invention is subjected to a preform process, the defect
percentage is about 1% or less. A decrease in the production yield
is undesirable because it may necessitate a reduction in the
productivity, e.g., a reduction in the process speed, in order to
reduce the defect.
[0098] When the heat shrinkable polyester film of the present
invention is formed into a label having a bonded portion
(backlining portion), the bonded portion of the label has an
adhesive retention of about 97% or more, preferably about 99% or
more, and more preferably about 99.5% or more, after shrinkage.
[0099] When the heat shrinkable polyester film of the present
invention is formed into a label, the label preferably has a
compressive strength of about 300 g or more, and more preferably
about 400 g or more. While the compressive strength is influenced
by the film thickness, the compressive strength is preferably about
300 g or more so that the film can suitably be used with a
high-speed label application machine. When the compressive strength
is less than 300 g, there may be a label application defective.
[0100] The thickness of the heat shrinkable polyester film of the
present invention is not limited to any particular value. As a heat
shrinkable film for use in a label, the thickness of the film is
preferably 10 .mu.m to 200 .mu.m, and more preferably 20 .mu.m to
100 .mu.m.
[0101] A cap sealing label can be produced as described above.
First, a sheet of heat shrinkable film having a predetermined size
is rolled into a tubular shape with two of its opposite edges
bonded together. Then, the tubular film is cut into smaller label
pieces. The method of bonding is not limited to any particular
method. For example, a solvent or a swelling agent is applied on at
least one of two opposite edges of the heat shrinkable polyester
film, the opposite edges are bonded together before the solvent or
the swelling agent dries up.
[0102] A halogenated hydrocarbon solvent is particularly
recommended for use in the above-described method. The halogenated
hydrocarbon solvent comprises low boiling point solvents as
follows. Such a low boiling point solvent comprises an aliphatic
and aromatic halogenated hydrocarbon, and has a boiling point of
200.degree. C. or less and a vapor pressure of 5 mmHg or more at
20.degree. C. Particularly, in view of the high-speed process, the
solvent preferably has a boiling point of 150.degree. C. or less
and a vapor pressure of 30 mmHg or more at 20.degree. C.
[0103] Specific examples of the solvent include a halogenated
aliphatic hydrocarbon (e.g., dichloromethane, chloroform,
dichloroacetylene, dichloroethylidene, di-chloroethylene,
1,1,1-trichloroethane, 1,1,2-trichloroethane,
1,1,2,2-tetrachloroethane, trichloroethylene, and dipropylene
chloride), a halogenated aromatic hydrocarbon (e.g.,
ortho-dichlorobenzene), and the like. It is understood that the
solvent used in the present invention is not limited to those
listed above. Any solvent may advantageously be used in the present
invention as long as it can dissolve the polyester composition of
the present invention and has a boiling point and a vapor pressure
as described above. Applicable solvents other than a halogenated
hydrocarbon solvent include, for example, aromatic hydrocarbons
(e.g., benzene, toluene, xylene, and trimethylbenzene), phenols
(e.g., phenol, and metacresol), alcohols (e.g., benzyl alcohol),
nitro hydrocarbons (e.g., a nitrobenzene), nitryl (e.g.,
acetonitrile), nitride compounds such as amines (e.g., normal
butylamine, pyridine, and morpholine), ketones (e.g., acetone,
methyl ethyl ketone, methyl isobutyl ketone, and
methylcyclohexane), a glycol ether (e. g., dioxane), an ether such
as furans (e.g., tetrahydrofuran), an ester (e.g., ethyl acetate,
normal butylacetate, andmonoethyl acetate), an organic acid (e.g.,
a formic acid, an acetic acid, and fluoroacetic acid), an inorganic
acid (e.g., a sulfuric acid, and a nitric acid), a sulfur
derivative (e.g., carbon disulfide), N,N-dimethylformamide, and the
like. Particularly, those with a high volatility are preferred.
Among ether solvents, a particularly useful solvent is dioxane.
[0104] The solvent or swelling agent preferably has a solubility
index in a range of 8.0 to 13.8. However, the solubility index is
not limited to this range. From a different point of view, the
solvent or swelling agent preferably is such that when the
polyester film having a size of 5 cm.times.1 cm.times.40 .mu.m is
immersed in the solvent or swelling agent at 23.degree. C. for 10
sec, the degree of swelling (as defined below) is 1% or more.
However, again, the degree of swelling is not limited to this.
[0105] Degree of swelling=((A-B)/B).times.100 (%), where
[0106] A: the thickness of the film after immersion
[0107] B: the thickness of the film before immersion
[0108] The above-listed solvents or swellings agent are merely
examples, and the present invention is not limited to those shown
above. Moreover, the solvents or swelling agents may be used alone
or in combination.
[0109] Next, a specific example of the method for producing a heat
shrinkable polyester film of the present invention will be
described, though the present invention is not limited to such a
method.
[0110] An undrawn film can be obtained by the same method as that
described above. The extrusion process may be done with any known
method such as a T-die method, or a tubular method.
[0111] The obtained undrawn film is then drawn at a temperature
equal to or greater than Tg-5.degree. C. and less than
Tg+15.degree. C. (where Tg is the glass-transition temperature of
the polyester) along the transverse direction (direction
perpendicular to the extrusion direction) by a drawing factor of
3.0 or more, and preferably 3.5 or more.
[0112] Then, a heat treatment is optionally performed at 70.degree.
C. to 100.degree. C. to obtain the heat shrinkable polyester
film.
[0113] The film may be drawn with a tenter only in the transverse
direction, or in two directions, i.e., in the transverse direction
and additionally in the longitudinal direction. Such a biaxial
drawing may be performed either with a successive biaxial drawing
method or a simultaneous biaxial drawing method. After this drawing
process, the film may optionally be further drawn in the
longitudinal or transverse direction.
[0114] In order to achieve the objects of the present invention, it
is more practical to have the main shrinkage direction along the
transverse direction. Therefore, an exemplary film production
method where the main shrinkage direction is along the transverse
direction has been described above. However, it is understood that
the main shrinkage direction may alternatively be along the
longitudinal direction, in which case the above-described method
can be used only with the drawn direction being rotated by 90
degrees.
[0115] In the present invention, an undrawn film obtained from a
polyester is preferably drawn at a temperature of equal to or
greater than Tg-5.degree. C. and less than Tg+15.degree. C.
[0116] It is not preferable to draw the film at a temperature less
than Tg-5.degree. C. In such a case, a sufficient heat shrinkage, a
feature of the present invention, may not be obtained, and further
the transparency of the obtained film may deteriorate.
[0117] It is also not preferable to draw the film at a temperature
of Tg+15.degree. C. or more. In such a case, the film may not have
a sufficient rigidity in high-speed processes, and further the film
may have a substantially increased thickness variation.
[0118] The heat shrinkable polyester film of the present invention
preferably has a film thickness distribution of 6% or less, and
more preferably 5% or less. The film thickness distribution can be
calculated based on the following expression: Thickness
variation=((maximum thickness-minimum thickness)/average
thickness).times.100 (%).
[0119] A three-color printing test is performed to evaluate the
shrunk finish property of the film. With a film having a thickness
distribution of 6% or less, it is easy to superimpose the colors on
one another. However, with a film having a thickness distribution
greater than 6%, the colors may not be desirably superimposed on
one another.
[0120] In order to reduce the thickness distribution of a heat
shrinkable polyester film, it is preferred to heat the film to a
predetermined temperature with hot air at a low flow rate such that
the heat transfer coefficient is 0.0013
cal/cm.sup.2.multidot.sec.multidot..degree. C. or less in a
pre-heat process, which is performed before the drawing process for
drawing the film with a tenter in the transverse direction.
[0121] In order to suppress generation of heat inside the film
associated with the drawing process and thus to reduce the film
temperature non-uniformity in the width direction, the heat
transfer coefficient in the drawing process should be 0.0009
cal/cm.sup.2.multidot.sec.multidot..- degree. C. or more, and
preferably 0.0011 to 0.0017
cal/cm.sup.2.multidot.sec.multidot..degree. C.
[0122] When the heat transfer coefficient in the pre-heat process
exceeds 0.0013 cal/cm.sup.2.multidot.sec.multidot..degree. C. or
when that in the drawing process is 0.0009
cal/cm.sup.2.multidot.sec.multidot..degree. C. or less, the
thickness is likely to be non-uniform. In such a case, when a
multi-color printing is performed on the obtained film, the colors
of a printed pattern may not be properly superimposed on one
another.
(EXAMPLES)
[0123] The present invention will now be described in greater
detail by way of examples. However, the present invention is not
limited to these examples, but other examples may be possible
without departing from the scope of the present invention.
[0124] The evaluation methods used in the present invention will
now be described with reference to Table 1 and Table 2 below.
[0125] (1) Heat Shrinkage
[0126] A sheet of film was cut into 10 cm'10 cm pieces, and
subjected to a no-load treatment in hot water at a temperature
.+-.0.5.degree. C. of a predetermined temperature so as to
heat-shrink the film. Then, the longitudinal and transverse
dimensions of the film were measured so as to obtain the heat
shrinkage of the film according to the following expression
(Expression 1). The direction along which the heat shrinkage was
greater was assumed to be the main shrinkage direction of the
film.
Heat shrinkage={(length before shrinkage-length after
shrinkage)/length before shrinkage).times.100 (%) (Expression
1)
[0127] (2) Refractive Index
[0128] An Abbe refractometer was used to measure the refractive
index of the film along the longitudinal, transverse and thickness
directions of the film.
[0129] In Table 1 below, the refractive index of the film along the
longitudinal direction (main shrinkage direction) is denoted by Nx,
and the refractive index along the transverse direction (direction
perpendicular to the main shrinkage direction) is denoted by
Ny.
[0130] (3) Solvent Adhesiveness
[0131] The film was rolled into a tubular shape with two of its
opposite edges bonded together with 1,3-dioxolane. The tubular film
was cut into smaller pieces (samples) each having a width of 15 mm
in a transverse direction which is perpendicular to the direction
along which the film runs through the processing system. The bonded
portion was pulled along the transverse direction and peeled apart.
In the column "Solvent adhesiveness" in Table 1, ".largecircle."
indicates a sample which had a sufficient peel resistance.
[0132] (4) Shrunk Finish Property
[0133] Each sample was placed around commercially available food
container cans ("Friskie" manufactured by Friskie) and passed
through Universal Shrinker (Model: K2000) manufactured by Kyowa
Denki for a shrinker passage time of 15 sec (zone 1
temperature/zone 2 temperature)=(170.degre- e. C./170.degree. C.)
to shrink the sample onto the cans. The finish property of each
shrunk sample was evaluated as follows (10 samples were evaluated).
After the evaluation, each sample was marked as follows.
[0134] .largecircle.: No apparent defect observed
[0135] .times.: Crease or insufficient shrinkage observed
[0136] (5) Vibration Test
[0137] Referring to FIG. 1, each film sample was rolled into a tube
1, with two of its opposite edges being bonded together, and then
the tube 1 was placed around a vertical stack 2 (total weight: 660
g) of three food container cans each having a diameter of 72 mm and
a height of 55 mm. The can stack 2 with the tube 1 placed
therearound was passed through a shrink tunnel to shrink the tube 1
onto the can stack 2. Then, as shown in FIG. 2, a total of 18 packs
of such can stacks 3 were placed into a cardboard box 4 having a
length of 455 mm, a width of 230 mm and a height of 165 mm (6 packs
in the length direction by 3 packs in the width direction), and the
cardboard box 4 was sealed.
[0138] The cardboard box 4 was vibrated along the longitudinal
direction (indicated by arrow A in the figure) for 30 min by a
stroke of 50 mm and at a vibration rate of 180 reciprocations/min,
after which the transverse tearage of the tube 1 was visually
observed.
[0139] Referring to FIG. 3, the defect percentage (%) was
determined based on the number of defective packs per 18 packs,
wherein the defective pack was any pack having a tear flaw 6 whose
length ("L" in FIG. 3)is 30 mm or longer in a film 7 along a
periphery of the can 5. Then, a sample having a defect percentage
of 20% or less was marked ".largecircle.", and a sample having a
defect percentage exceeding 20% less was marked ".times.".
[0140] (6) Actual Shipping Test
[0141] Three of such cardboard boxes 4 as described above in the
section "Vibration test" were transported by land over a
predetermined distance. The defect percentage (%) was determined
based on the number of defective packs per 54 packs. Then, a sample
having a defect percentage of 20% or less was marked
".largecircle.", and a sample having a defect percentage exceeding
20% less was marked ".times.".
[0142] (7) Adhesive Retention of Bonded Portion (Backlining
Portion)
[0143] A heat shrinkable polyester film was passed through a tube
production apparatus, where 1,3-dioxolane was applied over a width
of 2 mm on one side of the film at one edge. Immediately, the film
was rolled into a tubular film and the edge was bonded onto the
opposite edge. The tubular film was cut into smaller pieces to
obtain a label 8 having a diameter of 87 mm and a length of 53 mm
as shown in FIG. 4A. As shown in FIG. 4B, the label 8 was placed
around a metal cylinder 9 having a diameter of 46 mm, and the label
8 was heat-shrunk onto the metal cylinder 9 through a process at a
temperature of 200.degree. C. for 2 sec. Then, the condition and
the strength of a bonded portion 10 were evaluated (a total of 200
(1000) samples were evaluated). In FIG. 4B, the length L.sub.1 was
47 mm, the length L.sub.2 was 6 mm, and the width of the bonded
portion 3 was 5 mm. The evaluation was done by visual observation
with the criteria shown below. The following expression (Expression
2) was used to obtain the adhesive retention of the bonded portion
(backlining portion).
Adhesive retention of the bonded portion (backlining
portion)=((number of samples evaluated.times.number of
defectives)/number of samples evaluated).times.100(%) (Expression
2)
[0144] (Criteria)
[0145] A sample was considered defective if, after shrinkage,
peeling had occurred in an upper portion 10a, in a lower portion
10b, or generally along the entire length of the bonded portion 10.
A sample was also considered defective if, after shrinkage, the
upper portion 10a and/or the lower portion 10b could be easily
peeled by hand. Otherwise, the sample was considered
non-defective.
[0146] FIG. 5A shows a case where peeling occurred in the lower
portion lob of the label 8. FIG. 5B shows a case where peeling
occurred in the upper portion 10a of the label 8.
[0147] (8) Preform Finish Property and Defect Percentage
[0148] For each of the shrunk labels evaluated as described in
section (7) above, the shrink property and the finish property of
the entire label including the bonded portion were evaluated(a
total of 200(1000) samples were evaluated). The evaluation was
conducted by visual observation with the criteria shown below.
Then, the preform finish defect percentage (total number of samples
evaluated=1000) was obtained by the following expression.
Preform finish defect percentage=(number of defectives/number of
samples evaluated).times.100 (%)
[0149] After the evaluation, each sample was marked as follows.
[0150] .largecircle.: No crease, no jumping, or no insufficient
shrinkage observed
[0151] .times.: Crease, jumping, or insufficient shrinkage
observed
[0152] FIG. 5C shows a case where jumping occurred in the sample.
FIG. 5D shows a case where crease occurred in the sample. FIG. 5E
shows a case where insufficient shrinkage occurred in the
sample.
[0153] (9) Shrinkage after Preform Process
[0154] For each of the shrunk labels evaluated as described in
section (7) above, the bonded portion (backlining portion) 10 was
cut off from the label 8, and the remainder was cut into pieces
each having a size of 100 mm along the main shrinkage direction by
40 mm along the direction perpendicular to the main shrinkage
direction. The label pieces were further heat-shrunk through a
no-loadtreatment in hot water at a temperature of 80.+-.0.5.degree.
C. for 5 sec. Then, the length of each label piece along the main
shrinkage direction and that along the perpendicular direction were
measured. The shrinkage after a preform process was obtained by the
following expression (Expression 3).
Shrinkage after preform=((length before shrinkage.times.length
after shrinkage)/length before shrinkage).times.100(%) (Expression
3)
[0155] (10) Tg (Glass-Transition Temperature)
[0156] DSC (model: DSC220) manufactured by Seiko Instruments &
Electronics Ltd was used to raise the temperature of an undrawn
film (10 mg) from -40.degree. C. to 120.degree. C. at a temperature
rising rate of 20.degree. C./min to obtain an endothermic curve.
The glass-transition temperature of the film was obtained based on
the obtained endothermic curve. A tangential line was drawn
immediately before and after an inflection point along the
endothermic curve to obtain Tg (glass-transition temperature) at
the intersection between the tangential lines.
[0157] (11) Film Haze
[0158] "1001DP" manufactured by Nihon Denshoku Kogyo was used to
measure the haze of each film sample in compliance with JIS
(Japanese Industrial Standards) K 7105.
[0159] The following polyesters (Polyesters A-E) were used in the
examples and comparative examples to be described below.
[0160] Polyester A: polyethylene terephthalate (intrin-sic
viscosity (IV): 0.75 dl/g)
[0161] Polyester B: a polyester comprising 100 mol % of
terephthalic acid, 70 mol % of ethylene glycol, and 30 mol % of
neopentyl glycol (IV: 0.72 dl/g)
[0162] Polyester C: polybutylene terephthalate (IV: 1.20 dl/g)
[0163] Polyester D: a polyester comprising 100 mol % of
terephthalic acid, 85 mol % of butanediol, and 15 mol % of
polytetramethylene glycol (molecular weight: 1000) (IV: 1.50
dl/g)
[0164] Polyester E: a polyester elastomer comprising a copolymer
polyester of 70 wt % of Polyester C and 30 wt % of
.epsilon.-caprolactone (reduced viscosity (.eta..sup.sp/c): 1.30
dl/g)
(Example 1)
[0165] A polyester obtained by mixing together 37 wt % of Polyester
A, 53 wt % of Polyester Band 10 wt % of Polyester C, as shown in
Table 1, was melted and extruded through a T die at a temperature
of 280.degree. C., and rapidly cooled down by using a chill roll to
obtain an undrawn film. The undrawn film was drawn in the
longitudinal direction by a drawing factor of 1.1 by using a
multi-stage roll type vertical drawer (roll temperature: 80.degree.
C.), and then drawn with a tenter in the transverse direction at
the film temperature of 73.degree. C. by a drawing factor of 3.9.
The film was then subjected to a heat treatment at 82.degree. C.
for 10 sec to obtain a heat shrinkable polyester film having a
thickness of 45 .mu.m.
(Examples 2-4 and Comparative Examples 1-4)
[0166] A heat shrinkable polyester film having a thickness of 45
.mu.m was obtained in a manner similar to that of Example 1 except
that different polyester ratio and drawing conditions were used as
shown in Table 1.
[0167] The evaluation results for the respective films of Examples
1-4 and Comparative Examples 1-4 are shown together in Table 1.
1 TABLE 1 Film production condition Longitudinal Transverse
Material drawing drawing Hot water shrinkage Polyester Polyester
Polyester Drawing Drawing Drawing Drawing 95.degree. C. .multidot.
10 sec (%) A B C temperature factor temperature factor Longitudinal
Transverse Example 1 37 53 10 80 1.1 73 3.9 14.0 62.0 Example 2 37
53 10 80 1.3 77 3.9 21.0 64.0 Example 3 30 60 10 80 1.2 77 3.9 18.0
65.0 Example 4 26 50 24 80 1.3 77 3.9 19.0 70.0 Comparative 37 53
10 -- (1.0) 73 3.9 7.0 60.0 example 1 Comparative 26 50 24 80 1.1
77 3.9 13.0 70.0 example 2 Comparative 10 66 24 80 1.2 78 3.9 15.0
68.0 example 3 Comparative 15 75 10 80 1.2 76 3.9 16.0 74.0 example
4 Shock Shock resistance resistance Refractive Shrunk in in index
Solvent finish vibration actual Nx Ny-Nx adhesiveness property test
shipping Example 1 1.562 0.061 .largecircle. .largecircle.
11.largecircle. .largecircle. Example 2 1.563 0.050 .largecircle.
.largecircle. 11.largecircle. .largecircle. Example 3 1.562 0.055
.largecircle. .largecircle. 17.largecircle. .largecircle. Example 4
1.563 0.060 .largecircle. .largecircle. 17.largecircle.
.largecircle. Comparative 1.560 0.072 .largecircle. .largecircle.
56X X example 1 Comparative 1.560 0.068 .largecircle. .largecircle.
56X X example 2 Comparative 1.561 0.044 .largecircle. .largecircle.
44X X example 3 Comparative 1.558 0.059 .largecircle. .largecircle.
50X X example 4
(Example 5)
[0168] A polyester composition obtained by mixing together 36 wt %
of Polyester A, 49 wt % of Polyester B and 15 wt % of Polyester E,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0169] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 65.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Example 6)
[0170] A polyester composition obtained by mixing together 36 wt %
of Polyester A, 49 wt % of Polyester B and 15 wt % of Polyester E,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0171] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 70.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Example 7)
[0172] A polyester composition obtained by mixing together 26 wt %
of Polyester A, 54 wt % of Polyester B and 20 wt % of Polyester E,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0173] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 65.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Example 8)
[0174] A polyester composition obtained by mixing together 26 wt %
of Polyester A, 54 wt % of Polyester B and 20 wt % of Polyester E,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0175] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 70.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Comparative Example 5)
[0176] A polyester composition obtained by mixing together 26 wt %
of Polyester A, 45 wt % of Polyester B, 24 wt % of Polyester C, and
5 wt % of Polyester D, as shown in Table 2, was melted and extruded
through a T die at a temperature of 280.degree. C., and rapidly
cooled down by using a chill roll to obtain an undrawn film.
[0177] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 68.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Comparative Example 6)
[0178] A polyester composition obtained by mixing together 26 wt %
of Polyester A, 50 wt % of Polyester B and 24 wt % of Polyester C,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0179] The undrawn film was pre-heated until the film temperature
reached 80.degree. C., after which the film was drawn with a tenter
at a temperature of 65.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
(Comparative Example 7)
[0180] A polyester composition obtained by mixing together 7 wt %
of Polyester A, 68 wt % of Polyester B and 25 wt % of Polyester C,
as shown in Table 2, was melted and extruded through a T die at a
temperature of 280.degree. C., and rapidly cooled down by using a
chill roll to obtain an undrawn film.
[0181] The undrawn film was pre-heated until the film temperature
reached 80.degree. C. after which the film was drawn with a tenter
at a temperature of 75.degree. C. in the transverse direction by a
drawing factor of 4.0 to obtain a heat shrinkable polyester film
having a thickness of 50 .mu.m.
[0182] The evaluation results for the respective films of Examples
5-8 and Comparative Examples 5-7 are shown together in Table 2.
2 TABLE 2 Adhesive Preform Material Film production retention
finish Shrinkage Poly- Poly- Poly- Poly- Poly- condition Shrinkage
(%) of Preform defective after Film ester ester ester ester ester
Drawing Drawing (5 sec) backlining finish percentage preform haze A
B C D E temperature factor 70.degree. C. 95.degree. C. portion
property (%) (%) (%) Example 5 36 49 0 0 15 65 4.0 30.0 68.0 95.0
.largecircle. 0.5 20.0 8 Example 6 36 49 0 0 15 70 4.0 23.0 63.0
97.0 .largecircle. 1.0 16.0 7 Example 7 26 54 0 0 20 65 4.0 35.0
67.0 99.0 .largecircle. 0.5 22.0 5 Example 8 26 54 0 0 20 70 4.0
27.0 61.0 99.5 .largecircle. 1.0 18.0 4 Comparative 26 45 24 5 0 68
4.0 30.0 65.0 90.0 .largecircle. -- 20.0 13 example 5 Comparative
26 50 24 0 0 65 4.0 35.0 74.0 95.0 X 2.0 31.0 7 example 6
Comparative 7 68 25 0 0 75 4.0 21.0 68.0 99.0 X 5.0 33.0 5 example
7
[0183] As is apparent from Table 1, each of the heat shrinkable
polyester films obtained in Examples 1-4 exhibits a good shrunk
finish property (no defects such as insufficient shrinkage, crease,
distortion are observed), a good solvent adhesiveness, a good shock
resistance in the vibration test and a good shock resistance in the
actual shipping test.
[0184] Thus, the heat shrinkable polyester film of the present
invention is a film having a high quality and a high practicability
which is suitable as a multi-packaging label for cans and can be
used under low temperatures.
[0185] On the contrary, the heat shrinkable polyester films
obtained in Comparative Examples 1-4 exhibited a poor shock
resistance. Thus, each of the heat shrinkable polyester films of
the comparative examples exhibited a poor quality and a poor
practicability.
[0186] As is apparent from Table 2, for each of the films obtained
in Examples 5-8, the bonded portion (backlining portion) of the
label produced from the film exhibited a high adhesive retention.
Each of the films also exhibited a good shrunk finish property. The
films obtained in Examples 5-8 exhibited a low film haze and a good
transparency. Moreover, the films obtained in Examples 5-8
exhibited a hot water shrinkage after a preform process of 15% to
30% along the main shrinkage direction for a hot water process at
80.degree. C. for 5 sec. The labels of Examples 5-8 also exhibited
a good shrunk finish property.
[0187] The heat shrinkable polyester film of the present invention
has a high quality and a high practicability, and is particularly
suitable as a cap sealing label.
[0188] On the contrary, for each of the heat shrinkable films
obtained in Comparative Examples 5-7, the bonded portion
(backlining portion) of the label produced from the film exhibited
a poor adhesive retention. Moreover, the film obtained in
Comparative Example 5 exhibited a high film haze and thus a poor
transparency. Moreover, each of the films obtained in Comparative
Examples 6 and 7 exhibited a high hot water shrinkage after a
preform process, and a poor shrunk finish property. Thus, each of
the heat shrinkable polyester films obtained in Comparative
Examples 5-7 had a poor quality and a low practicability.
[0189] Thus, the heat shrinkable polyester film of the present
invention has a good shock resistance during shipping especially
under low temperatures, with a good finish after shrinkage and a
sufficient solvent adhesiveness.
[0190] Therefore, the heat shrinkable polyester film of the present
invention is suitable for use in a multi-packaging label for
packaging, inter alia, a stack of cans.
[0191] The present invention also provides a heat shrinkable
polyester film suitable for use in a label, especially, a cap
sealing label for a bottle container, or the like.
[0192] When the heat shrinkable polyester film of the present
invention is used as a cap sealing label, the bonded portion
(backlining portion) of the label has a high adhesive retention
after shrinkage and has very little crease, shrinkage
non-uniformity, distortion, or jumping occurring from a shrinkage
process. Thus, the heat shrinkable polyester film of the present
invention is very useful as a cap sealing label.
[0193] Various other modifications will be apparent to and can be
readily made by those skilled in the art without departing from the
scope and spirit of this invention. Accordingly, it is not intended
that the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
* * * * *